How to make characters interact
This is no different than any other type of animation, you need to plan the animation make a storyboard and animate the characters using animation tools. That includes changing properties of your character's rig control objects and keying them at different times, may include various simulations as well. This is an extremely wide question. Answering it fully could possibly require a few books of text. 

My advice would be to start with planing the animation itself and making a storyboard and possibly an animatic(a video with drawings from the story boards that tests the timing and rythm before you start animating - like this). You will need to make sure your characters are rigged well, or rig them yourself. Rigging is another wide topic that cannot be explained in a few words and you would need to research that on your own. It needs to be done well and cannot be skipped. For the animation itself my advice would be to use as much reference as possible. Film your friends if needed and try to copy timing and movement - do not attempt to come up timing using your imagination - that would be a mistake and you would most certainly fail without reference. Always use reference or base your decisions on observation. As far as tools in Blender go, it would not be logical to expect a description of everything that is needed in an answer here. You need to learn it and that requires a lot of research, time and effort so it is good to be prepared for that. Learning to animate well will take many years, however I believe you can learn the basics in a few hundred hours of hard work. YouTube is a good resource. You can start by watching tutorials on animating in Blender there.